The first eclipse photograph was taken in 1851. In 1860, chiefly owing to the labours of Mr. De La Rue, our knowledge was enormously increased. The Kew photoheliograph was the instrument used, and the series of pictures obtained showed conclusively that the prominences belonged to the sun. In 1868 the prominences were again photographed. In 1869 the Americans attacked the corona, and their suggestion that the base of it was truly solar has been confirmed by other photographs taken in 1870, 1871, and 1875. Although to the eye the phenomena changed from place to place, to the camera it was everywhere the same with the same duration of exposure. * * * * * It is not to be wondered at, then, that on the occasion of the last transit of Venus, which may be regarded as a partial eclipse of the sun, photography was suggested as a means of recording the phenomena. Science is largely indebted to Dr. Janssen, Mr. De La Rue, and others for bringing celestial photography to aid us in this branch of work also. While on the one hand astronomers have to deal with precious moments, to do very much in very little time, in circumstances of great excitement; the photographer on the other goes on quietly preparing and exposing his plates, and noting the time of the exposure, and thus can make the whole time taken by the planet in its transit over the sun’s disc one enormous base line. His micrometrical measures of the position of the planet on the sun’s disc can be made after all is over. It was suggested by Dr. Janssen that a circular plate of sufficient size to contain sixty photographs of the limb of the sun, at the points at which Venus entered and left it could be moved on step by step round its centre, and so expose a fresh surface to the sun’s image focussed on it, say every second. In this way the phenomena of the transit were actually recorded at several stations. * * * * * [Illustration: FIG. 213.—Part of Beer and Mädler’s Map of the Moon. ] With reference to the moon, we have said enough to show that if we wish to map her correctly, it is now no longer necessary to depend on ordinary eye observations alone; it is perfectly clear that by means of an image of the moon, taken by photography, we are able to fix many points on the lunar surface. Still, although we can thus fix these and use them as so many points of the first order, as one might say, in a triangulation, there is much that photography cannot do; the work of the eye observer would be essential in filling in the details and giving the contour lines required to make a map of the moon. The accompanying drawings on the same scale show that up to the present, for minute work, the eye beats the camera. [Illustration: FIG. 214.—The same Region copied from a Photograph by De La Rue. ]